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The periglacial environment in the Qarliturvik valley, Bylot Island (Nunavut) is characterized by the abundant presence of ice wedges polygons. Through those ice-rich networks, snowmelt water can trigger gully formation, initiated by convective heat flux between water and permafrost. The gullies strongly modify mass transfer (water, sediments, C, nutrients) in the geosystem. Permafrost degradation processes through thermo erosional gullying can reach fast and expanded scales; earlier studies revealed retreat rates of tens of meters in only a few weeks. However, stabilization mechanisms locally reduce erosion and lead to a re-aggradation of permafrost. The study focusses on the impacts of gully stabilization on the morphology and cryostratigraphy of permafrost, in a landscape evolution perspective. Preliminary results show that stabilized gullies are characterized by the formation of aggradational ice associated with the rising of the permafrost table. The study focusses specifically on one gully that has stabilized many decades ago. We will perform a 3D characterization of the gully and chronostratigraphical studies to determine the spatio-temporal context of erosion, stabilization and re-aggradation of permafrost. These data will be used to estimate the latent heat associated with the new ice volume of the upper part of the permafrost, together with the implications for the permafrost resilience to climate change and their role in the evolution of periglacial landscape.
The methodology will consist of a precise cartography of the morphology of a stabilized gully in extent and in depth, using a differential GNSS (Global Navigation Satellite System), in order to incorporate the data in a tridimensional geographic information system. Cryostratigraphic sequences will be collected by georadar surveys, using 50 and 200 MHz antennas to probe permafrost (0-8 m) through transversal sections of the gully. Moreover, the extraction of permafrost cores for validation of georadar probing data will allow us to build a tridimensional representation of the gully cryostratigraphy at and between the coring logs and to determine quantitatively in the laboratory volumetic ice contents. On a finer scale, we will analyze cryofacies of permafrost cores through computed tomography. This will allow us to see and analyze permafrost cryostructures, orientation of air bubbles indicating the freezing front propagation, together with the volumetric ice and sediment content. Radiocarbon dating of the organic matter from plants that colonized the gully will allow us to estimate the time scale required for the surface to stabilize. Finally, by using the cryostratigraphic model we will evaluate the amount of latent heat which lies in the upper part of permafrost of the transversal sections studied, key factor of the thermal and mechanical equilibrium of stabilized gullies.
The results of this study will allow us a better understanding of the role of ice formation in the spatiotemporal process of stabilization of thermo-erosion gullies within the periglacial landscape. The effects of such gullies on geosystems' energy and material flows is currently not taken into account in permafrost evolution models responding to climate changes.